AUTHOR=Macias Leslye , Mercado Víctor , Olmos Jorge 

TITLE=Assessment of Bacillus species capacity to protect Nile tilapia from A. hydrophila infection and improve growth performance

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=14

YEAR=2024

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2024.1354736

DOI=10.3389/fcimb.2024.1354736

ISSN=2235-2988

ABSTRACT=<p>The present study evaluated the capacity of three <italic>Bacillus</italic> species to improve health status and growth performance of Nile Tilapia fed with high levels of soybean meal and challenged with <italic>Aeromonas hydrophila</italic>. <italic>In vitro</italic> experiments showed that β-hemolysin and metalloprotease enzymes were produced <italic>by A. hydrophila</italic> throughout the exponential growth phase. <italic>In vivo</italic> experiments showed that 10<sup>7</sup> colony-forming units (CFUs)/ml of this pathogen killed 50% of control group fishes in 13 days. To evaluate the influence of <italic>Bacillus</italic> strains on health status and growth performance in Nile Tilapia, 180 fishes (33.44 + 0.05 g) were distributed in 12 tanks of 200 L each, and animals were fed twice per day until satiety. 1) Control group without <italic>Bacillus</italic>, 2) <italic>Bacillus</italic> sp1, 3) <italic>Bacillus</italic> sp2, and 4) <italic>Bacillus</italic> sp3 groups were formulated containing 10<sup>6</sup> CFU/g. After 40 days of feeding, the fishes were intraperitoneally injected with 1 ml of <italic>A. hydrophila</italic> at 2 × 10<sup>7</sup> CFU/ml, and mortality was recorded. The results showed that cumulative mortality rate was significantly (p&lt; 0.05) lower in the <italic>Bacillus</italic> sp1 (25%), sp2 (5%), and sp3 (15%) groups, than the control group (50%). Weight gain was also significantly better (p&lt; 0.05) in the <italic>Bacillus</italic> sp1 (36%), sp2 (67%), and sp3 (55%) groups with respect to the control group (30%). In conclusion, functional diet formulated with high levels of soybean meal and supplemented with <italic>Bacillus</italic> sp2 could be an alternative to protect Nile tilapia cultures from <italic>A. hydrophila</italic> infections and improve fish growth performance.</p>